This is a KBC 3.3/4 inch HSS straight flute shell reamer. Shell reamers are fluted almost their entire length, they have a tapered hole (1/8 inch per foot) which fits on a tapered arbor. The slots in the reamer engage lugs on the arbor providing ample strength of drive. If you have any questions, let us know. Our part number on this one is 5-150-245